Most of construction-related sludge (construction-related soil) produced as construction surplus soil in excavating work, dredging work and the like are transferred to a reclaimed land and the like to dispose as landfill. Among them, such soil regulated by a law for disposal as soil containing heavy metals such as chromium, cadmium and the like possibly discharged from tunneling work and the like or strongly acidic soil containing sulfur and the like is difficult to detoxify, so that at present it is filled in a pit, at bottom of which a water non-permeable sheet lies.
A cement-type solidifying agent is suitable for solidifying the inorganic soil (not containing polymer coagulants and the like), but has a high pH value and keeps a strong alkaline condition at pH 14 for a long hour exceeding a pH range of 3.5 to 10, at which an organism is habitable, so that utilization of the solidified substance obtained by such a solidifying agent is limited.
A lime-type solidifying agent is suitable to treat inorganic soil similarly to the cement-type solidifying agent, but causes a highly exothermic reaction in hydration reaction to generate a large volume of dust. The solidified substance obtained also has a high pH value similar to the cement and could not yield sufficient strength after solidification.
A gypsum-type solidifying agent has a low pH after solidification of the intended soil different from the cement-type and lime-type solidifying agents, so that the alkali-related pollution is difficult to take place but it could not produce sufficient strength after solidification.
Such solidifying agents have a common problem, in which when a hazardous substance is contained the intended soil, the hazardous component is suppressed to elute to some extent right after solidification, but an elutable hazardous component thereafter gradually elutes from the solidified substance and non-elution is thus difficult to maintain for an extended period of time. Improvement of a solidifying agent to solve such problems has been desired and development of a solidifying agent enabling to solidify any kind of soil fitting for the purpose as well as enabling to detoxify the hazardous substance and the like has been desired.